A casting ladle for a steel melt can comprise, as described in the aforementioned copending application and references of record in the file thereof, a spout or outlet through which the melt is to be discharged and generally in the form of an outlet sleeve, the lower end of which may be closed by, for example, a slider, valve plate or other plate-like closure.
As described in the aforementioned copending application, it is possible to separate the melt from the valve plate or slider by a flowable spout-filling mass of a refractory composition which prevents obstruction of the movement of the slider, readily is discharged from the spout when the slider is moved into its open position, but forms a cap or dome over the spout opening or sleeve by interaction of the steel melt with components of the spout-filling mass the cap being capable of preventing penetration of the melt into this mass and to the slider but being adapted to break away from the weight of the melt above this cap when the supporting mass is discharged in the open position of the slider.
The spout-filling mass can consist of chromium ore sand, i.e. a chromite sand rich in chromium oxide and especially Cr.sub.2 O.sub.3, quartz sand (predominantly consisting of SiO.sub.2) and a finely divided auxiliary substance which contributes to the cap formation by interaction with the melt.
The chromium ore component can make up less than 70% of the mixture and the auxiliary component is present in an amount by weight which is less than that of the chromium ore component and the quartz sand component.
The reference to the cap formation herein will be understood to signify that where the spout-filling mass comes into contact with the melt, i.e. at the interface between this mass and the melt, the spout-filling mass is sintered into a thin shell constituting the aforementioned cap which has a dome configuration able to withstand in part ferrostatic pressure of the melt as long as the spout remains filled with the comminuted but flowable portion of the mass, but which can rupture under the ferrostatic pressure when the slider is moved to its open position and the support of the mass below the cap is eliminated.
The proportions given herein are proportions by weight unless stated otherwise.
In the aforementioned copending application corresponding to German patent No. 32 14 168, a spout-filling mass is described which has been found to be highly effective in bringing about the cap formation as indicated above but which nevertheless allows a practically unlimited slider opening rate in the sense that discharge of the ladle with movement of the slider is not materially prevented, i.e. is 100%.
Apparently the cap formation is a result of a reduction of part of the chromium ore component with the carbon in this spout-filling mass at the interface thereof with the melt.
Care must be taken, of course, in such a system to ensure that excessive reduction of the chromium ore component does not occur and hence the chromium ore and carbon proportions must be designed for the particular purposes and indeed are especially established for various melts and ladle applications.
In general the carbon component should be about 3 to 10% of the spout-filling mass.
The presence of carbon in the spout-filling mass, however, can contribute to some carburization of the steel melt which is sometimes disadvantageous. Furthermore, when the carbon is in the mass in the form of a hydrocarbon, hydrogen is cracked from the carbon-containing component and can diffuse into the steel melt. This is detrimental especially to vacuum treated steels and can give rise to flocculation therein.